Ben, at Heresthethingblog.com answered my question. I hadn’t expected an answer, actually. But his website invited queries, and I was puzzled about the grayed out Back Arrow at the top of Safari, now that I’m using Mountain Lion. I was used to clicking that arrow to return to one of the sites I’d looked at earlier. He wrote right back and mentioned the browser tabs at the top of the page in Safari. Yes! That solves the question. I had not been using Tabs to go back to earlier sites. When the Back Arrow is grayed out, I can click on a previous Tab.

To close a Tab click the button that appears in the left of the tab when the cursor hovers over it. The + sign means add new webpage Tab, click to open a new tab. The black box means show all tabs, click to show tabs in Tab View. More to learn, but having fun!